It is well established that interaction between macrophages and breast carcinoma cells plays an important role in carcinogenesis. However, the precise role of proteases in this process has not yet been clearly elucidated. Thus, the aims of the present study were to determine whether interaction between breast carcinoma cell lines MDA-MB-231 and human monocyte cell line U937 may modulate expression of proteases responsible for extracellular matrix degradation, as well as to identify the major proteases secreted by monocytes/macrophages and breast carcinoma cells. We used secretions of MDA-MB-231 to activate and differentiate U937 into active monocytes/macrophages. Activated U937 were seeded in co-culture with MDA-MB-231 on three dimensional in-vitro tissue culture models that recapitulate tumor microenvironment. Live cell imaging proteolysis assay was used to determine the proteolytic activity and degradation of collagen by co-culture spheroid. Then transwell co-culture plates were used to identify major proteases expressed due to interaction between U937 cells and MDA-MB-231 cells. Imaging assay results demonstrated that co-culture of activated U937 and MDA-MB-231 induced proteolytic activity of the co-culture spheroid one fold more than that induced in co-culture of control U937 and MDA-MB-231. The increase in proteolytic activity of co-culture spheroid was due to the interaction between breast carcinoma cells and monocytes, which resulted in the increase in expression and activity of intracellular proteases by U937, as well as increase in expression and secretion of pericellular proteases by MDA-MB-231. Transwell co-culture assay results showed that interaction between U937 and MDA-MB-231 induced 1) expression and activity of intracellular cathepsin B (CTSB) in U937; 2) expression and activity of secreted gelatinases [matrix metalloproteinase-2 and 9 (MMP-2 and -9)] in MDA-MB-231 cells. In conclusion, paracrine interaction between breast carcinoma cells and activated monocytes/macrophages enhanced a proteolytic activity of the tumor microenvironment and degradation of the extracellular matrix proteins, which facilitates cancer growth and invasion.
Key words: Breast cancer- monocytes/macrophages- cathepsin B- matrix metalloproteinase
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